The provision of refrigeration, such as for the cooling and/or freezing of foods or pharmaceuticals, is typically carried out using a mechanical refrigeration system wherein a refrigerant such as ammonia or a freon is employed in a vapor compression cycle. Such systems are effective for providing refrigeration at relatively high temperature levels but to effectively achieve low level temperature refrigeration there generally is required vacuum operation and/or cascading which increases both capital and operating costs.
One method for more effectively providing refrigeration at low temperature levels is to use an expendable cryogenic liquid, such as liquid nitrogen, either separately or in conjunction with a mechanical refrigeration system, to provide the requisite low level refrigeration. However, such systems, while effective, are expensive because of the loss of, and therefore the need for continued replacement of, the cryogenic liquid.
Accordingly, it is an object of this invention to provide a method for providing refrigeration, such as to a heat exchanger or to an insulated enclosure, which can be used to effectively provide such refrigeration, when needed, at a low temperature.